Study On Chemical Structure And Mineral Evolution Of Coal Gangue During Pyrolysis And Combustion Characteristics Of Char

Coal gangue is a kind of combustible solid waste,which will cause environmental pollution and waste of resources.Its combustion and utilization can not only solve the problem of stacking,but also save coal consumption.Therefore,this paper intends to study the chemical structure,mineral evolution and combustion characteristics of char in the process of coal gangue pyrolysis,as to provide basic data and theoretical support for the combustion and utilization of coal gangue.Two kinds of coal gangues from Anyuan(Ay)and Huopu(HP)of Jiangxi Province were selected for the experiment,and the pyrolysis was carried out in N2 atmosphere to produce char(200-1000?).The chemical structure and minerals of coal gangue and its char were analyzed by FTIR,XRD,XPS and Raman spectra.The results show that most of the organic peaks in the infrared spectrum are covered by mineral peaks.With the increase of pyrolysis temperature,the relative contents of C-C,C-H and C-O decrease gradually,while the relative contents of C=O and O-C=O increase.In the range of 400-700?,due to the decomposition of organic matter,the defective carbon structure increases with the increase of temperature;in the range of 800-1000?,with the formation of tight aromatic ring,the order degree of carbon structure increases;the size of graphite microcrystalline plane is directly proportional to the order degree of carbon structure.The main mineral components of coal gangue are quartz,kaolinite,anatase,siderite,calcite,illite and muscovite.Kaolinite is decomposed into metakaolinite at 400-600?,and then mullite is formed at 900-1000?;siderite is decomposed into magnetite and magnetite at 400-600?,and the product is decomposed into iron rich spinel olivine(Fe2SiO4)with silicate at 800-1000?;illite is decomposed into mullite at 800-900?,and transformed into mullite at 900-1000?.The results of the thermogravimetry experiments of coal gangue and char show that with the increase of pyrolysis temperature of char,the combustion performance of char decreases as a whole due to the increase of volatile analysis and carbon structure order.In the initial stage of combustion,the original coal gangue and the char pyrolysised below 500? adsorbed oxygen,the TG curve increased,and the activation energy decreased.After heat treatment at 600? or above,the maximum weight loss rate of gangue increases due to the influence of pore structure.The existence of siderite results in the increase of combustion activation energy.But for the combustion of char pyrolysised at 500-800?,the activation energy and ignition temperature are significantly reduced due to the catalysis of decomposition product of siderite(magnetite).The results of the thermogravimetry of coal gangue combustion under different heating rates(10,20,30?/min)show that the combustion process of coal gangue is affected by the heating lag.The increase of heating rate makes the combustion area move to high temperature greatly,and the ignition and burnout temperatures increase,but the combustion reactivity increases.At the same time,the thermal hysteresis is related to the mineral composition of coal gangue,and the HP coal gangue with high iron mineral content has relatively small thermal hysteresis effect.